OLED display technology has the benefit of a wide operating temperature range, low power consumption, wide viewing angle, high contrast and fast response time making it the best choice for large area displays. While the demand for these displays continues to increase, the technology still remains expensive to produce and lacks in overall resolution and performance quality.
Traditional OLED displays include a stack of thin layers formed on a substrate. A light-emitting layer of a luminescent organic solid, as well as adjacent semiconductor layers, is sandwiched between a cathode and an anode. The light-emitting layer may be selected from any of a multitude of fluorescent and phosphorescent organic solids. Any of the layers, and particularly the light-emitting layer, also referred to herein as the emissive layer or the organic emissive layer, may consist of multiple sublayers. In an active-matrix organic light-emitting diode the cathode may include a metal electrode having low work function, and the anode may include a transparent electrode made from, for example, indium tin oxide (ITO) or.
In a typical OLED, either the cathode or the anode is transparent. Evaporation, spin casting, other appropriate polymer film-forming techniques, or chemical may form the films self-assembly. Thicknesses typically range from a few monolayers to about 1 to 2,000 angstroms. Protection of OLED against oxygen and moisture can be achieved by encapsulation of the device. The encapsulation can be obtained by means of a single thin-film layer situated on the substrate, surrounding the OLED.
In an OLED device, when an electric current is applied across the device negatively charged electrons move into the organic material(s) from the cathode. Positive charges, typically referred to as holes, move into the organic material(s) from the anode. The positive and negative charges meet in the center layers (i.e., the semiconducting organic material), combine, and produce photons. The wavelength, and consequently the color, of the photons depends on the electronic properties of the organic material in which the photons are generated. Pixel drivers can be configured as either current sources or voltage sources to control the amount of light generated by the OLEDs in an AMOLED display.
The color of light emitted from the organic light-emitting device can be controlled by the selection of the organic material. Generating blue, red and green light simultaneously may produce white light. Other individual colors, different than red, green and blue, can be also used to produce in combination a white spectrum. Specifically, the precise color of light emitted by a particular structure can be controlled both by selection of the organic material, as well as by selection of dopants in the organic emissive layers. Alternatively, filters of red, green or blue, or other colors, may be added on top of a white light-emitting pixel. In other examples, white light emitting OLED pixels may be used in monochromatic displays.
High-resolution active matrix displays may include millions of pixels and sub-pixels that are individually addressed by the drive electronics. Each sub-pixel can have several semiconductor transistors and other IC components. Each OLED may correspond to a pixel or a sub-pixel. Generally, however, an OLED display consists of many OLED pixels, and each OLED pixel may have three sub-pixels associated with it, in which each sub-pixel may include red, green and blue color OLEDs or may emit white light, which be filtered to either red, green or blue.
Some structures for forming a full color image using an OELD device are generally known. For example, as shown in FIG. 1A, an independent red, green, blue (RGB) layer structure uses three organic luminescent layers 20, 22, and 24 independently coated on a substrate 10 for emitting red, green, and blue light respectively. As shown in FIG. 1B, a color transformation structure uses color transformation layers 30, 32, and 34 interposed between the substrate 10 and a blue luminescent layer 36. As shown in FIG. 1C, a color filter structure uses color filters 40, 42, and 44 for emitting the red, green and blue light respectively. The color filters 40, 42, and 44 are interposed between the substrate 10 and a white organic luminescent layer 46.
When using the independent RGB layer structure shown in FIG. 1A, the RGB material is deposited and patterned using a shadow mask. As a result, although there is high light efficiency, the red, green and blue light cannot be minutely separated from each other. The color transformation structure shown in FIG. 1B requires that an organic fluorescent material is deposited on the substrate by an exposure process, thereby adding a process step for forming the full color image. In addition, when using the color transformation structure, it is difficult to coat the color transformation layer with a uniform thickness. When using the color filter structure shown in FIG. 1C, the color filter is formed through a conventional photolithography process. As a result, a relatively higher resolution display panel is manufactured using the color filter structure and the color filter structure is more widely used than the other structures.
The OLED display of the present invention utilizes a new OLED architecture with a unique pixel design and pattern of electrode connections through vias. A “via” is a vertical electrical connection between different layers of conductors in a physical electronic circuit. In the present invention, electrical connections to and from OLED displays are provided to each anode line and cathode line by at least one via. Each via is formed of a column of conductive material or in its simplest form provided as an opening leaving free access to the electrode beneath.
One method used to fabricate large area displays is referred to as tiling. In tiling, a plurality of smaller displays are arranged in a matrix to create large, high-resolution, multi-panel displays. Typically, tiling to obtain large area displays rely upon the stitching of multiple tiles together, wherein each tile has a pixel or an array thereof. However, the edge line of these assembled tiled displays produce visually disturbing seams, resulting from the gaps between adjacent pixels on adjacent tiles. The interconnections necessary to supply signals to the display may also be noticeable, distract the viewer, and otherwise detract from the overall visual appearance of the image. Therefore, it is desirable to fabricate tiled, high-resolution, micro-panel displays, which do not have noticeable or perceptible seams under the intended viewing conditions.
Flat-panel displays (FPDs) provide the best choice for constructing “seamless”, tiled screens however, FPDs depend on the micro fabrication of components that carry the pixel patterns, which are not viable for very large displays. Therefore, the inventors have determined that tiles with arrays of OLED pixels can be micro fabricated and then assembled together to form a larger area electronic display. The present invention provides unique designs and methods for achieving such large, seamless, tiled panels for full color, high-resolution large area displays. In particular, these large area displays measure approximately 1 to 3 inches per side and are ideal for, amongst other things, high-resolution displays in demand for virtual reality device (e.g. headsets).
Early image sensor technology was manufactured using micron lithography such that an entire wafer was exposed in a single shot. During that time, feature sizes were large and wafers small enough so that a photomask as large as the wafer itself could project onto the wafer precisely enough to reproduce the required features. Once silicon processes were used for submicron feature sizes and wafer sizes increased, image sensors could no longer be made as large as the wafer itself in one shot. Lithography moved to smaller masks and wafer exposure to “step and repeat” methods, such that a single exposure could only result in a device in the order of 25 mm×25 mm. This created the need for stitching, which was developed in order to build a device from a sequence of exposures resulting in a device much larger than the size of a single mask. A typical pixel array is formed from blocks of a few thousand pixels. The mask contains a single instance of this block, and by stepping the mask the equivalent of the block size, the pixel block can be repeated side by side on the surface of the wafer. Multiple dies can be formed on the wafer and in some cases, multiple die patterns can be included in a single reticle to reduce the cost of the reticle set. The circuitry that surrounds the pixel is then added to complete the device. Using this method, a single mask can be used to manufacture large area devices.
It is a primary object of the present invention to provide a large area display comprised of more than one AMOLED microdisplay panel fabricated using a single reticle to create a variety of different display devices with different configurations.
It is another object of the present invention to provide a large area display preferably comprised of, but not limited to, four AMOLED microdisplay panels arranged together which are independently addressable and avoid the necessity of stitching together layers.
It is another object of the present invention to provide a high-resolution display comprised of more than one AMOLED microdisplay for use in virtual reality, high-speed and/or head mounted devices and applications.